<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <style>
        div{
            width: 400px;
            height: 200px;
            border: 1px solid chocolate;
            margin: 20px;
        }

        .bg{
            background-image: radial-gradient(circle, black 10%, transparent 20%);
            background-size: 20px 20px;
        }
    </style>
    <div class="bg"></div>
</body>
</html>